Body self-hydrophobic polypropylene fiber / cellulose / graphene composite paper as well as preparation and application thereof

Abstract

The invention belongs to the technical field of fuel cells, and discloses bulk self-hydrophobic polypropylene fiber / cellulose / graphene composite paper and preparation and application thereof. The preparation method comprises the following steps: 1) modifying PP fibers by adopting cationic polyacrylamide to obtain modified PP fibers; 2) preparing graphene, cellulose fibers and modified PP fibers into slurry; carrying out papermaking molding, acid pickling and hot press molding on the pulp to obtain composite paper; and 3) performing laser drilling on the composite paper. The composite paper disclosed by the invention has high conductivity, high mechanical strength and uniform body hydrophobicity, the breakthrough pressure of water is remarkably reduced, the water-gas transmission efficiency is optimized, and the composite paper is used for a gas diffusion layer of a proton exchange membrane fuel cell, so that the performance and durability of a device can be effectively improved. The composite paper disclosed by the invention is also used for electrochemical energy devices for water and gas management.

Description

Technical Field

[0001] This invention belongs to the field of functional materials and energy devices, specifically relating to a bulk self-hydrophobic polypropylene (PP) fiber / cellulose / graphene composite paper, its preparation method, and its application. Background Technology

[0002] In fuel cells or some electrochemical energy devices with efficient water and gas management, carbon fiber paper is generally used as the substrate. However, there are some shortcomings when using carbon fiber paper as the substrate, such as: low mechanical strength and easy cracking; poor hydrophobicity, requiring hydrophobic agent treatment, but the hydrophobicity of the substrate surface is uneven; and the conductivity needs to be improved.

[0003] When carbon fiber paper is used in proton exchange membrane fuel cells (PEMFC), the gas diffusion layer (GDL) of the PEMFC is usually made of carbon fiber paper as the substrate and surface-treated with a fluorinated hydrophobic agent (such as PTFE). However, the traditional gas diffusion layer has the following key defects: (1) It requires multiple impregnation-hot pressing cycles (such as impregnation with 5% PTFE solution 3 to 5 times), resulting in high energy consumption. (2) Performance bottlenecks: ① Uneven hydrophobicity: PTFE only adheres to the surface, and the internal pores are hydrophilic, resulting in a water breakthrough pressure as high as 8754Pa, causing water flooding and oxygen transport resistance (limiting current density <1.0A / cm). 2 ); ② Low mechanical strength: The tensile strength of commercial carbon paper (TGP-H-060) is only 19MPa, which makes it brittle; ③ Poor stability: PTFE is prone to aging in acidic environments (pH≈2~3), and its performance degrades by more than 20% after 5000 cycles of accelerated stress testing. Summary of the Invention

[0004] To overcome the shortcomings and deficiencies of existing technologies, the present invention aims to provide a bulk-based self-hydrophobic polypropylene fiber / cellulose / graphene composite paper, its preparation, and its applications. The composite paper of the present invention utilizes a wet-process papermaking technique combined with modified polypropylene (PP) fibers to construct a three-dimensional network structure, achieving high conductivity, high mechanical strength, and uniform hydrophobicity. When used in fuel cells, it can significantly improve fuel cell performance and durability. The composite paper of the present invention is used to prepare the gas diffusion layer (GDL) of a proton exchange membrane fuel cell (PEMFC). The composite paper of the present invention can also be used in other electrochemical energy devices requiring efficient water and gas management.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for preparing a bulk-based self-hydrophobic polypropylene fiber / cellulose / graphene composite paper includes the following steps:

[0007] 1) PP fibers are modified with cationic polyacrylamide (CPAM) to obtain modified polyacrylamide fibers, i.e., modified PP fibers;

[0008] 2) Graphene, cellulose fiber and modified PP fiber are mixed into a pulp; then the pulp is made into paper, pickled, and hot-pressed to obtain composite paper;

[0009] 3) Laser perforation is performed on the composite paper to obtain a bulk self-hydrophobic polypropylene fiber / cellulose / graphene composite paper with a microporous structure.

[0010] The amounts of graphene, cellulose fiber, and modified PP fiber used are as follows: by mass percentage.

[0011] Graphene: 30%–60%; Cellulose fiber: 30%–50%; Modified polypropylene fiber: 5%–25%.

[0012] The mass ratio of graphene to cellulose fiber is (1.1-2):1, preferably (1.2-1.7):1.

[0013] The graphene has a sheet thickness of 1–5 nm and a specific surface area ≥ 500 m². 2 / g. Prepared using a redox method.

[0014] The cellulose fiber is made from hardwood pulp with a beating degree of 40–50°SR and a carboxyl content of 0.5–1.2 mmol / g. The fiber length of the cellulose fiber is 0.5–2 mm.

[0015] The PP fiber has a length of 3-5 mm and a diameter of 10-30 μm.

[0016] In step 1), the amount of cationic polyacrylamide (CPAM) used is 0.1% to 0.5% of the mass of PP fiber.

[0017] The specific preparation steps of the modified polypropylene fiber are as follows: PP fiber is mixed with CPAM solution and stirred. After modification, the Zeta potential of the fiber changes from negative to positive. The mass concentration of the CPAM solution is 0.5%–1.5%.

[0018] The slurry described in step 2) contains water, and the total solid content of graphene, cellulose fiber and modified PP fiber in the slurry is 5% to 8%.

[0019] Papermaking parameters: Papermaking speed: 10-20 m / min; Mesh count: 70-90 mesh; Basis weight: 115-125 g / m 2 Thickness 180~220μm.

[0020] The pickling refers to treatment with nitric acid followed by washing until neutral. The mass concentration of the nitric acid is 10-20%. The treatment time is 20-40 minutes.

[0021] The hot pressing conditions are: 265–280℃, 4.5–5.5 MPa, and hot pressing time of 8–12 minutes. Preheating for 2–4 minutes is performed before hot pressing, followed by the application of pressure.

[0022] The pore structure has a pore diameter of 100–160 μm, a pore spacing of 400–500 μm, and a pore density of 50–60 pores / cm³. 2 .

[0023] The bulk self-hydrophobic polypropylene fiber / cellulose / graphene composite paper is used to prepare the gas diffusion layer of a proton exchange membrane fuel cell.

[0024] The method for preparing the gas diffusion layer for a proton exchange membrane fuel cell includes the following steps:

[0025] S1) PP fibers are modified with cationic polyacrylamide (CPAM) to obtain modified polyacrylamide fibers (i.e., modified PP fibers);

[0026] S2) Graphene, cellulose fiber and modified PP are mixed into a pulp; then the pulp is made into paper, pickled, and hot-pressed to obtain composite paper;

[0027] S3) Laser perforation of the composite paper;

[0028] S4) Spray the coating slurry onto the surface of the laser-perforated composite paper, and heat-treat it to obtain a gas diffusion layer.

[0029] The conditions in steps S1 to S3 are the same as in steps 1) to 3) of the preparation method of bulk self-hydrophobic polypropylene fiber / cellulose / graphene composite paper.

[0030] The spraying slurry mentioned in step S4 is obtained by dispersing carbon black and PTFE emulsion in a mixed solvent of isopropanol / water;

[0031] The volume ratio of isopropanol to water is 4:1; the concentration of PTFE emulsion is 5 wt%; and the mass ratio of carbon black to PTFE emulsion is 7:3.

[0032] The spraying is ultrasonic spraying. The spraying thickness is 50-80 μm.

[0033] The heat treatment involves calcining at 310–330°C under a protective atmosphere for 1.5–2.5 hours.

[0034] The protective atmosphere is nitrogen.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] (1) The composite paper of the present invention has the property of being self-hydrophobic and has an overall hydrophobic network: after the PP fiber is hot-pressed and melted, the hydrophobic alkyl chain (-CH2-CH2-) is uniformly distributed in the interior of the material, which reduces the pressure and is significantly better than the traditional surface hydrophobic solution.

[0037] (2) In the composite paper of the present invention, graphene and PP fibers are continuously distributed, which gives the composite paper an excellent conductive network; and the PP cross-linking network inhibits the brittle fracture of cellulose, thereby enhancing the mechanical properties of the composite paper.

[0038] (3) The present invention adopts an integrated wet papermaking-hot pressing-laser perforation process, which does not require multiple impregnations or complex post-treatments. The method of the present invention is simple.

[0039] (4) The composite paper of the present invention can be used in fuel cells to significantly improve fuel cell performance and durability. Attached Figure Description

[0040] Figure 1 A comparison of the pore size distribution of the microporous composite paper prepared in Example 3 with that of commercial carbon paper (Toray TGP-H-060);

[0041] Figure 2 The tensile property curves of the composite paper with microporous structure prepared in Examples 1-5;

[0042] Figure 3 The water contact angle of the composite paper with microporous structure prepared in Examples 1-5;

[0043] Figure 4 The voltage-current density curves of the gas diffusion layer GDL prepared in Examples 1-5 in the fuel cell;

[0044] Figure 5 The power density-current density curves of the gas diffusion layer GDL prepared in Examples 1-5 in the fuel cell;

[0045] Figure 6 The conductivity diagrams are for the gas diffusion layers (GDLs) prepared in Examples 1-5.

[0046] Figure 7 The figure shows the durability test results of the gas diffusion layer GDL prepared in Example 3 in a fuel cell;

[0047] Figure 8 The polarization curves are for Example 3 and Comparative Example 1 (PTFE modified carbon paper). Detailed Implementation

[0048] The present invention will now be described in detail with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments. In the embodiments, graphene is used in the form of graphene slurry, which is a commercially available aqueous dispersion with a concentration of 5 wt%.

[0049] Example 1: Modified PP fiber content 5%

[0050] A method for preparing a bulk-based self-hydrophobic polypropylene fiber / cellulose / graphene composite paper includes the following steps:

[0051] (1) PP fiber modification: Polypropylene fiber (PP fiber, length 3mm, diameter 20μm) was mixed with 1wt% CPAM solution and mechanically stirred for 30 minutes (500rpm). After modification, the Zeta potential changed from negative to positive. The amount of CPAM added was 0.3% of the oven-dry weight of PP fiber.

[0052] (2) Wet papermaking process:

[0053] (2-1) Graphene (in the form of graphene slurry with a concentration of 5 wt%), cellulose fiber (hardwood pulp) and modified PP fiber are formulated into a slurry with a total solid content of 6%. Water may be added during the formulation process. Graphene: 57 wt%; Cellulose fiber: 38 wt%; Modified PP fiber: 5 wt%.

[0054] (2-2) Papermaking process: The pulp is formed into paper; papermaking speed: 15m / min, wire count: 80 mesh; basis weight: 120g / m 2 Thickness 200μm;

[0055] (3) Acid treatment: Immerse the composite paper in 15wt% nitric acid solution for 30 minutes, and rinse with deionized water until neutral (conductivity <10μS / cm);

[0056] (4) Hot pressing: The acid-treated composite paper is hot pressed; Hot pressing conditions: 270℃, 5MPa, preheated for 3 minutes and then hot pressed for 10 minutes;

[0057] (5) Laser drilling: The hot-pressed composite paper is laser-drilled; the hole diameter is 150μm, the hole spacing is 450μm, and the through-hole density is 50 holes / cm. 2 A self-hydrophobic polypropylene fiber / cellulose / graphene composite paper with a microporous structure was obtained.

[0058] The bulk self-hydrophobic polypropylene fiber / cellulose / graphene composite paper is used to prepare GDL.

[0059] GDL Assembly: (1) Disperse carbon black and PTFE emulsion in a mixed solvent of isopropanol / water to obtain a spray slurry; the volume ratio of isopropanol / water is 4:1; the concentration of PTFE emulsion is 5wt%; and the mass ratio of carbon black and PTFE emulsion is 7:3.

[0060] (2) Spray the coating slurry onto the surface of the composite paper and calcine it at 320°C for 2 hours to obtain a gas diffusion layer.

[0061] Example 2: PP fiber content 10%

[0062] (1) 10wt% PP fiber, other conditions are the same as in Example 1.

[0063] (2) Wet papermaking: Pulp ratio: graphene 54wt%, cellulose fiber 36wt%, PP fiber 10wt%, total solids content 7%. Other conditions are the same as in Example 1.

[0064] (3)~(5) Same as Example 1.

[0065] GDL assembly is the same as in Example 1.

[0066] Example 3: PP fiber content 15%

[0067] (1) 15wt% PP fiber, other conditions are the same as in Example 1.

[0068] (2) Wet papermaking: Pulp ratio: graphene 51wt%, cellulose fiber 34wt%, PP fiber 15wt%, total solids content 8%. Other conditions are the same as in Example 1.

[0069] (3)~(5) Same as Example 1.

[0070] GDL assembly is the same as in Example 1.

[0071] Example 4: PP fiber content 20%

[0072] (1) 20wt% PP fiber, other conditions are the same as in Example 1.

[0073] (2) Wet papermaking: Pulp ratio: 48wt% graphene, 32wt% cellulose fiber, 20wt% PP fiber, total solid content 7.5%. Other conditions are the same as in Example 1.

[0074] (3)~(5) Same as Example 1.

[0075] GDL assembly is the same as in Example 1.

[0076] Example 5: PP fiber content 25%

[0077] (1) 25wt% PP fiber, other conditions are the same as in Example 1.

[0078] (2) Wet papermaking: Pulp ratio: 45wt% graphene, 30wt% cellulose fiber, 25wt% PP fiber, total solids content 8%. Other conditions are the same as in Example 1.

[0079] (3)~(5) Same as Example 1.

[0080] GDL assembly is the same as in Example 1.

[0081] Comparative Example 1: Traditional PTFE-modified carbon paper GDL

[0082] Commercial carbon paper (Toray TGP-H-060) was impregnated with 2 wt% PTFE emulsion, and impregnated repeatedly until the PTFE loading reached 10 wt%; calcined at 320°C for 2 hours; a microporous layer was sprayed (carbon black and PTFE were mixed, and the spraying slurry was the same as in Example 1; loading was 2 mg / cm³). 2 ).

[0083] Figure 1 A comparison of the pore size distribution of the microporous composite paper prepared in Example 3 with that of commercial carbon paper (Toray TGP-H-060);

[0084] Figure 2 The tensile property curves of the composite paper with microporous structure prepared in Examples 1-5;

[0085] Figure 3 The water contact angle of the composite paper with microporous structure prepared in Examples 1-5;

[0086] Figure 4 The voltage-current density curves of the gas diffusion layer GDL prepared in Examples 1-5 in the fuel cell;

[0087] Figure 5 The power density-current density curves of the gas diffusion layer GDL prepared in Examples 1-5 in the fuel cell;

[0088] Figure 6 The conductivity diagrams are for the gas diffusion layers (GDLs) prepared in Examples 1-5.

[0089] Figure 7 The figure shows the durability test results of the gas diffusion layer GDL prepared in Example 3 in a fuel cell;

[0090] Figure 8 The polarization curves are for Example 3 and Comparative Example 1 (PTFE modified carbon paper).

Claims

1. A method for preparing a bulk self-hydrophobic polypropylene fiber / cellulose / graphene composite paper, characterized in that: Includes the following steps: 1) PP fibers are modified with cationic polyacrylamide to obtain modified polyacrylamide fibers, i.e., modified PP fibers; 2) Graphene, cellulose fiber and modified PP fiber are mixed into a pulp; then the pulp is made into paper, pickled, and hot-pressed to obtain composite paper; 3) Laser perforation is performed on the composite paper to obtain a bulk self-hydrophobic polypropylene fiber / cellulose / graphene composite paper with a microporous structure. The amounts of graphene, cellulose fiber, and modified PP fiber used are as follows: by mass percentage. Graphene: 30%–60%; Cellulose fiber: 30%–50%; Modified PP fiber: 5%–25%; The mass ratio of graphene to cellulose fiber is (1.1–2):1; The hot pressing conditions are: 265–280℃, 4.5–5.5MPa, and hot pressing time of 8–12 min; The pore structure has a pore diameter of 100–160 μm, a pore spacing of 400–500 μm, and a pore density of 50–60 pores / cm³. 2 .

2. The method for preparing the bulk self-hydrophobic polypropylene fiber / cellulose / graphene composite paper according to claim 1, characterized in that: The mass ratio of graphene to cellulose fiber is (1.2–1.7):1; The amount of cationic polyacrylamide used in step 1) is 0.1% to 0.5% of the mass of PP fiber; In step 3), holes are punched to form a through-hole array.

3. The method for preparing the bulk self-hydrophobic polypropylene fiber / cellulose / graphene composite paper according to claim 1, characterized in that: The graphene has a sheet thickness of 1–5 nm and a specific surface area ≥ 500 m². 2 / g; The cellulose fiber is made from hardwood pulp with a freeness of 40–50°SR and a carboxyl content of 0.5–1.2 mmol / g. The PP fiber has a length of 3-5 mm.

4. The method for preparing the bulk self-hydrophobic polypropylene fiber / cellulose / graphene composite paper according to claim 1, characterized in that: The specific preparation steps of the modified polypropylene fiber described in step 1) are as follows: PP fiber is mixed with CPAM solution and stirred. The Zeta potential of the modified fiber changes from negative to positive. The mass concentration of CPAM solution is 0.5-1.5%.

5. The method for preparing the bulk self-hydrophobic polypropylene fiber / cellulose / graphene composite paper according to claim 1, characterized in that: The slurry described in step 2) contains water, and the total solid content of graphene, cellulose fiber and modified PP fiber in the slurry is 5% to 8%. Papermaking parameters: Papermaking speed: 10-20 m / min, mesh count: 70-90 mesh; Quantitative dose: 115~125g / m 2 Thickness 180~220μm; drying temperature 80~100℃, drying time 5~10 minutes; The pickling refers to treatment with nitric acid followed by washing until neutral; the mass concentration of the nitric acid is 10-20%; the treatment time is 20-40 minutes. Preheat for 2-4 minutes before hot pressing, then apply pressure for hot pressing; The laser drilling uses a fiber laser with a power of 20-50W, a scanning speed of 100-200mm / s, a pulse frequency of 20-50kHz, and a single hole processing time of 0.5-2 seconds.

6. A bulk self-hydrophobic polypropylene fiber / cellulose / graphene composite paper obtained by the preparation method according to any one of claims 1 to 5.

7. The application of the bulk self-hydrophobic polypropylene fiber / cellulose / graphene composite paper according to claim 6, characterized in that: The bulk self-hydrophobic polypropylene fiber / cellulose / graphene composite paper is used to prepare the gas diffusion layer of a proton exchange membrane fuel cell.

8. A gas diffusion layer for a proton exchange membrane fuel cell, characterized in that: The gas diffusion layer is obtained by spraying a coating slurry onto the surface of the self-hydrophobic polypropylene fiber / cellulose / graphene composite paper as defined in claim 6, followed by heat treatment; the coating slurry is obtained by dispersing carbon black and PTFE emulsion in a mixed solvent of isopropanol / water.

9. The gas diffusion layer of the proton exchange membrane fuel cell according to claim 8, characterized in that: The volume ratio of isopropanol to water is 4:1; the concentration of PTFE emulsion is 5 wt%; and the mass ratio of carbon black to PTFE emulsion is 7:

3. The spraying is ultrasonic spraying; the spraying thickness is 50-80 μm. The heat treatment involves calcining at 310–330°C under a protective atmosphere for 1.5–2.5 hours.

10. The application of the gas diffusion layer according to claim 8 or 9, characterized in that: The gas diffusion layer is used in a proton exchange membrane fuel cell; the gas diffusion layer serves as the gas diffusion layer for the cathode and / or anode. Or the gas diffusion layer is used in electrochemical energy devices for water vapor management.

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